Formulation of optimized excavatable cement treated materials using a new punching test apparatus

摘要

Classical techniques for backfilling of trenches use unbounded materials. Unfortunately, they have been presenting several drawbacks regarding compaction such as noise disturbance, time of implementation and long-term settlement. In that context, controlled low strength materials could be a good alternative solution thanks to their fluidity and cementitious setting, provided that they remain excavatable, even manually with a pick. In fact, it is essential to ensure a rapid and easy permanent access to the underlying networks, in case of emergency or maintenance. Yet, the excavatability was not well defined, nor well measured so far. A fortiori, no mix design process is available to control the excavatability of these materials. It is the purpose of this article to develop one. Recently, a new approach based on a simple punching test in laboratory was proposed to provide a quantitative characterization of cement treated materials excavatability, accounting for the pick impact energy (Morin in Study of cementitious material excavatability, 2009; Morin et al. in Eur J Environ Civ Eng 17(10):935-955, 2013; Can Geotech J, 2017. https://doi.org/10.1139/cgi-2016-0534). The present paper first briefly describes how, in the continuation of this study, the testing set-up was improved, the approach was validated and the underlying theoretical models were calibrated on an important campaign of manual excavation on real scale trenches, in parallel with laboratory punching tests. Once the laboratory method developed, it was possible to proceed a large parametric campaign at the laboratory stage to identify the mix design parameters that influence the excavatability of cementitious materials. The second part of the paper describes the methodology used and the empirical model deduced to link the mix proportions of a cementitious material to its excavatability. Finally, manual excavations were realized on real scale trenches to confirm the relevance of the model. In conclusion, a global mix design method is proposed for excavatable cement treated materials, with a brief economical simulation.